text:
Where is the safest seat in the plane?
If I'm going on holiday with my family on an airliner such as one of the ones listed on this page, then where is the safest place to sit?
The answers to this question seem to imply that the seats at the rear of the plane would be safer:
Why are flight recorders generally located in the tail?
but of course I can think of quite a few things which might make it different for passengers versus the flight recorder.
I realise that flying is statistically a lot safer than driving, so I don't need to be told not to worry about safety - I'm not worrying, I'm just interested in the difference in safety between different seats in the airliner. Because if I get a choice of seats then (ceteris paribus) I can't see any reason not to choose the safer ones.
I'm guessing it might be affected by things like proximity to the exits, and so might be different in different models of airliner. If that's the case then can you tell me what factors affect the safety of each seat? E.g. is it more important to be close to an exit or to be further back in the plane? What should I look for?
Is it different on long-haul versus short-haul? Or are there other differences in the type of flight (and therefore the more typical type of accident) which change the 'safest place to sit'?

A few articles I've found on the topic:
 - Popular Mechanics, 2007 (statistical review: back is safest)
 - Discovery / Channel 4, 2013 (one-off crash experiment: back is safest)
 - BBC, 2014 (expert opinion: no safest place)
 - CAA, 2006 (statistical review of evacuations: exit rows and adjoining rows are safest)

Ceteris paribus, there is a reason to choose the (very slightly) more dangerous ones, since you get to leave the plane earlier. On a large plane (eg the A380), getting to the checkpoint earlier could save you up to half an hour in immigration.

@MarchHo, those seats being the ones at the front?

Rather than focusing on an exit, knowing in advance where are all the exits can help. You don't know in advance whether the overwing exit you are sitting next to will be usable in an event (e.g. if there's an engine fire, that overwing exit wouldn't be used).

inb4 "inside the flight recorder".

What is the value of such analysis? I mean if I count the number of fatalities and injuries in a frontal collision in a car, what I'll obtain is the largest number is for the front left seat, with an exception for the right front one in some countries (India, UK). Does that prove this seat is the most dangerous? Not at all! It happens this seat is the most used, because this is the driver seat, and most cars carry no passengers. So what about the result of the airplane studies? How do they manage such obstacles? How do we identify the ones which don't manage them?

@mins, you make a good point. Ideally we'd be talking per-hours-of-seat-occupancy or per-trip-where-seat-is-occupied or something like that (IMO).

While there isn't any such thing as "safest seat", in general middle seats in a 3 seat row are of course not the best. Also seats near the emergency exits are more safe than other seats when it comes to quickly evacuating the plane.

Before I start, remember that we're talking about statistics of location in the aircraft, within statistics of survival of an accident (95%), which is itself dependent on a statistic of particular type of accident (approx 85% have no fatalities at all), within something which is already a very unlikely event (an aviation accident).
So let us for a moment assume that you're in a semi-survivable accident, ie where there are a mixture of fatalities and survivors - this is already a very unlikely scenario... in the vast majority of accidents either everybody dies (rare), or nobody does (most common).
To give you the straight out answer to your question, in such an accident, the rear of the plane is safest - more passengers have survived plane crashes in those seats than any other. This is due to most accidents being nose-first, so if it's going to be partially survivable your ideal location is near the back: the front of the aircraft essentially acting like a crumple zone. Thus, if an accident is survivable, you are more likely to survive in the back of the aircraft.
Of course, every accident is different - if your aircraft runs off the runway and spins, the back can impact first. Similarly if your aircraft stalls and pitches up. Alternately you could slew sideways into another aircraft in a taxiway etc etc... but in most cases, the impact is more likely to be nose-first, thus the rear is the safest place.
Also statistically, being near to a door but not next to a window gives the "optimum" chance of survival - more people survive in such locations. This is due to ease of evacuation (being near the aisle and the exit), and without being whacked in the head by a crumpling fuselage.
So if you're going on purely "increasing your chances", a non-window seat near the rear door is the best possible place to be in an accident... other than on the ground, having missed your plane.
The thing to remember, though, is that (referring to modern aviation)

Accident rates work out as roughly 1-per-1 million flights
Around 85-87% of aviation accidents involve no fatalities (so fatal accidents are around 15-per-100 million flights)
Even if you're in a crash where someone dies, Aviation accidents with fatalities have a fatality rate of somewhere between 5% and 25% (which is to say, even if we only look at accidents where one or more people do die, 75-95% of people in those accidents survive).

So that gives you a 1/4th to 1/20th of a chance of a 3/20th of a chance of a 1 in a million chance of becoming a statistic in my next post on this subject. So that would take you somewhere between 20 and 100 million flights before you die.
You have a 1-in-100-million chance of being in a fatal accident, and even then you a 75-95% chance of surviving it anyway.
So in short, if it's going to get you it will, if it's not it won't. By the time you've survived enough accidents for it to be anything more then sheer atrocious luck that you die at all, you'd already have developed a healthy fear of flying and have gathered enough air miles to take a taxi....

on the ground having missed your plane. Yup, that's the safest spot of all! Well done!!

What can I say, I don't like to tempt statistics, even if we're talking 1-in-100million

"By the time you've survived enough accidents for it to be anything more then sheer atrocious luck that you die at all, you'd already have developed a healthy fear of flying and have gathered enough air miles to take a taxi...." -- +1 :)

@BrianS and you've also lived several pilot's worth of lives.

@FreeMan - I'd suggest that on the ground, having missed your plane might imply you're driving/taxiing back to your point of origin, which would increase your fatality potential dramatically more than having caught your flight :) being on the roadway and all, no?

@Mikey it might also imply that you're standing at the gate watching the plane being pushed back while banging your head on any handy hard surface. Which would also mean that you're likely safer on the plane, but yeah...

Also, @JonStory, having just reread this, "which is to say, 75-95% of everyone who is in a fatal accident, survives" reads really funny. I know what you mean, but it could come across as "75-95% of people who are fatally shot survive". I know you mean that "75-95% of the people who are in aircraft accidents in which there are fatalities aren't one of those fatalities", but it's more amusing my way. :)

@FreeMan haha yeah I can see how that could come across like that... it's kind of an awkward sentence to write because the concept is strange (basically, accidents where someone dies still only have a 5-25% fatality rate on average) but I've had a got at improving it

@JonStory I've read this Q&A several times and this is the first time that jumped out at me, so it was obviously pretty clear what you meant the first time. I think my brain's already on vacation, so it's seeing things differently. That said, your updated wording is much more explicit and leaves no room for creative and/or humorous interpretation. Which may or may not be better. ;)

There is no general safe or unsafe seat rule - it really depends on the circumstances of any mishap. If the plane runs into a mountain, the rear seats give you more crush zone, so the deceleration is lower and stretched out over time to sustainable levels. However, if the plane comes in too low during landing and strikes ground first with the tail, those rear seats will see the highest acceleration.
You might as well look into the historical records of the particular type of aircraft - see this question for some numbers. However, to use this as the basis of a risk assessment would be an abuse of statistics.
Another factor might be the airline: How well do they maintain the aircraft, and how well are the pilots prepared to handle an emergency? There are multiple studies which look into the different cultures around the world and how much they contribute to the accident rate. Some report a tripling of accidents between the unsafest and the safest cultures.
I expect that by choosing a safe airline you will have the highest influence on the safety of the trip, but unfortunately the desire of passengers to pick the cheapest flights no matter what has led operators to cut corners wherever they can.

'Choosing a safe airline' is pretty difficult, as a passenger it's hard to make that comparison. Are safety ratings like these reasonably well-correlated with the likelihood of an accident? Or with the possibility of surviving if there is an accident? Or should I be looking at something different?

@AE: This would probably deserve asking as a separate question.

@AE: Generally, aircraft accidents are so uncommon that one single incident will jumble all those rankings. However, the linked list looks reasonable. In the end, much will depend on factors beyond your control. Compare AF447 and UN232 - the pilots made all the difference, but you cannot choose the individual pilot.

@PeterKämpf, so bearing that in mind, does the passenger's choice of airline really make a material difference to their safety?

@AE: Yes, statistically it does. However, there are many more risks in life. If you look at the likelihood of dying in a car crash or by overeating, and you take precautions proportionally to their probability, you should spend 364 days of the year worrying about all other risks in life.

@PeterKämpf, yeah, I've already read all the car test reports and bought a Volvo, this is my one day a year for thinking about air travel. ;)

@PeterKämpf Intellectual curiosity surely is an adequate reason to ask questions here. I've wondered about this before myself, but that doesn't mean that I'm worried about crashing.

if the plane comes in too low during landing and strikes ground first with the tail, those rear seats will see the highest acceleration. It appears that even in that case in a seat with a seat belt on was a pretty safe place to be - the stew...flight attendants all survived, though with some injury. The goobers who didn't have their seat belts on were ejected from the plane and died.

@FreeMan: Right, and the energies involved are lower. One of the casualties was actually run over by a rescue vehicle and probably still alive before. The rear seats are indeed safer in almost all cases, especially when the emergency exit is close. But the choice of airline makes a bigger difference in my eyes.

The tail strike in Asiana B772 seems like a very unusual kind of tail strike, because (IIUC) the back of the plane hit the edge of the dock: "touched down short of runway 28L impacting the edge separating the runway from the San Francisco Bay". Presumably a 'normal' tail strike is less bad?

@AE: Yes, regular tail strikes happen when the angle of attack is too high during landing and are more tail scrapes than strikes. But it can also be quite severe.

Keep in mind that there is such a thing as a low-cost airline with an excellent safety record.  Example: Southwest Airlines, which has been responsible for exactly two deaths in nearly half a century of operations (one was an occupant of a car struck by a 737 that had run off the end of the runway, while the other was a passenger who died of injuries after the other passengers objected to his attempting to break into the cockpit).

Well, more for Southwest now with the engine failure that blew out a window and partially pulled a woman out a window.  But overall, airlines are pretty safe overall. How many tens of thousands a flight a year vs how many accidents, likely counted on just 2-3 hands total worldwide?

This Info-graphic will answer all your questions

So basically sit at the back of a Boeing 777 during April or May and avoid Aeroflot.

Welcome to Aviation.SE. Please be aware the image-only answer are generally not well received. Please consider including the relevant information in your post and eventually provide the image (with source!) as a reference.

This infographic is also very poorly controlled for variables, with the "dangerous airlines" section being the worst offender.

It really is a bad infographic. Of course the months with the most flights would have the most fatal accidents. That doesn't mean that you will be more safe by waiting until a month with fewer average accidents.

As the wonderful Aviation After-Dinner speaker David Gunson used to say, "You should always sit at the back as no aircraft had yet been known to reverse into a mountain." This was, of course, before the Osprey made it a possibility.

Just based on your articles I guess it is fairly straightforward to pick a seat with high survivability:
Behind the wings, close to an emergency exit
However, keep in mind that if your family has small children, or if you worry a lot about things like what the safest seat in a plane is, you may want to avoid sitting next to emergency exits. They are used best if the person next to them keeps their head cool and opens it in times of crisis.
As such the best seat for you may be the row next to the emergency exit.

You may want to sit next to the aisle, but then again you probably gain more by letting each child be accompanied by an adult, so this is only relevant if there are more than 2 seats next to each window.

Also, nearest to the wings is also least disturbing to the middle-ear, and young one's may be subject to air-sickness if you sit far from the wings.

@Arluin How is sitting close to the wing "least disturbing to the middle-ear"? Ear problems come from altitude-related pressure changes, which are the same throughout the plane.

Pitching of the plane (nose up/down) rotates around the wings. At the wings there's very little movement compared to the extremities (front/rear). Seats at the front and rear move much farther up and down during pitch than those at the wings. Also yaw (turning left and right) pivots the plane at the middle. So again the seats in the middle of the plane don't move far during yaw, but those at the nose and tail move the farthest.

Studies vary, but they generally tend to converge on 3 items:

Aisle seats are safer* than window seats.
Seats at the rear are safer* than seats in the front.
Seats near emergency exits are safer* than those farther away.

Deducing from this and combining all 3 elements, an aisle seat at the back near an emergency exit seems to be the statistically safest* choice.
*(statistically higher survival rate)
Caveat: Single crashes are hardly meaningful, as most factors are idiosyncratic (type of impact, passenger distribution, particularly with regard to health and age, etc.) but they should even out across a large enough sample size.

Studies reaching the aforementioned conclusions:

Based on an analysis of the seating charts from more than 100 plane
  crashes, Professor Galea found that people seated within 5 rows of
  a serviceable exit were most likely to escape. Beyond 5 rows and your
  chances of survival are much lower. To stand the best chance of survival,
  book an exit row seat, or 1 row away. Many passengers survive the initial
  impact but don’t get off the plane quickly enough – and it’s the first 90
  seconds after a crash that are considered the most important by safety
  experts.
Passengers in aisle seats were also more likely to survive than those
  in window seats .
  (source 1) (source 2)

The rear cabin (seats located behind the trailing edge of the wing)
  had the highest average survival rate at 69%. The overwing section had
  a 56% survival rate, as did the coach section ahead of the wing.
  First/business-class sections (or in all-coach planes, the front 15%)
  had an average survival rate of just 49%.

Survival rates for various parts of the passenger cabin, based on an analysis of all commercial jet crashes in the United States since 1971 where detailed seating charts were available. (source)

In April 2012, a group of scientists remotely piloted an airplane and performed a staged crash in Mexico. The aircraft they used was an unmanned Boeing 727-200, fitted with numerous cameras, sensors, and crash test dummies. They simulated the most likely type of aircraft crash landing, a controlled but too fast decent where the plane flew straight into the ground.
Each seat and it's 'passengers' had sensors on them that demonstrated the amount of stress on that point of the plane during impact. The program seemed to conclude that in that type of crash, again the most common type to occur, the front and back 25% of the aircraft was the most severely affected and where the majority of the fatalities / serious injuries would occur. The middle of the plane, particularly those just over the wing faired the best. There is of course no way to predict what could happen, every plane and situation completely different.
The whole thing was filmed for television, an interesting watch although if you are a nervous flyer probably to be avoided! I believe it was called 'Curiosity: Plane Crash'

That's this TV show which I linked to in the question. The dummies at the front of the aircraft fared worst, those at the back of the aircraft came off best.  http://en.wikipedia.org/wiki/2012_Boeing_727_crash_experiment#Study_result

Though an analysis of a single crash is hardly decisive, its findings did support a study by Popular Mechanics, carried out in 2007. The magazine analysed all crashes since 1971 and found that those in rear seats (behind the wing’s trailing edge) were safest – survival rates were 69 per cent as opposed to 56 per cent over the wing and 49 per cent for those at the front of the plane.

Yes, that's the 2007 Popular Mechanics statistical review I linked to in the question.


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How do flight crew train/demonstrate ditching evacuation?
In case of evacuation, flight crew can train and demonstrate their ability with a real plane and test passengers.
However; how can one be trained in case of ditching ?
Obviously, it would be quite problematic to ditch an aircraft just for training/demonstration purpose...

Emergency Water Evacuation Drill and Air Crash Drill video.

Flight crew training facilities have a big pool with a mock aircraft hull with slides and rafts.
Real aircraft are rarely used for training. It's much cheaper to build a fake aircraft interior into the building and use that than to tie up an aircraft that should be making money. It also lets the instructors simulate more dangerous scenarios, like smoke in the cabin, safely.

The facility could also be the airline renting out a local swimming pool for training; they don't necessarily own their own pool.

Another example of the training, this time at an airline-owned facility.

Actually, the FAA offers underwater egress training as a safety seminar.  Around here it is offered in a high school pool, with a fake aircraft.  You get will get totally wet, but it is good training.  I first took a predecessor of this course about 35 years ago, when the Coast Guard offered it.
Look it up on the FAASTeam website, but here is an older link:
https://www.faasafety.gov/SPANS/event_details.aspx?eid=10024
One thing I keep in mind is that most of the water I fly over is 42F in the summer and colder in the winter.  Not quite as nice as a pool.  But going through the training, even if you don't like it, is a good experience to have when one is evaluating risks of overwater flights.

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How does an aircraft report crew programming of the FMS to the ground?
I am reading in the news that the MH370 flight changed its course by "Computer entry" and that it was programmed into the computer at least 12 minutes before the last voice contact with the plane.
How can they know that the change in the computer was done 12 minutes before (while the plane was still flying as on the original course)? And how do they know it was done in the computer, rather than the pilot steering manually?

The aircraft's Flight Management System (FMS) can be loaded with software that periodically sends position reports and flight tracking data to ground stations via ACARS.  If the particular software in use sends the full flight plan or at least the next few fixes periodically with estimated times, this would expose any changes in the flight plan to the dispatch office.
The incident flight in question had its ACARS turned off at some point and the "12 minute" figure is probably derived from the time between the last ACARS message being received and the radar observed turn off course initiated.   They would not be able to know exactly when the buttons on the FMS were pressed, but they could narrow the time down to a range when information changed between two automated reports sent via ACARS.
Relevant chronology:
01:07 final ACARS transmission
01:19 final voice communication

Interval: 12 minutes.

My guess is the "reporter" didn't know what they were reporting. As far as I know you don't need the FMS to change the heading the autopilot uses. The autopilot can be controlled by the FMS but the autopilot can be used independently.

@rheitzman it is true you can change heading with the autopilot alone but if you are flying a course 99% of us will put the fixes into the FMS for the autopilot to fly.

The earlier report referred to in the question has been contradicted by a later report. This undermines the premise of the question. Currently (24/3/2014) it appears there is no evidence that any change in flight-path was entered into the flight management system.

Malaysian officials, in a written update Sunday on the search, cast doubt on the theory that someone, perhaps a pilot, had reprogrammed the aircraft to make an unexpected left turn during the flight.
"The last ACARS transmission, sent at 1:07 a.m., showed nothing unusual. The 1:07 a.m. transmission showed a normal routing all the way to Beijing," it read.

CNN March 24, 2014 at 0225 GMT

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Has there even been a case of pilot incapacitation due to food poisoning?
On commercial flights, pilots are usually required to have different meal, to reduce the chance of food poisoning affecting both pilots.
Is this just a precautionary measure, or has this actually occurred?

May be a Duplicate

Have you never seen this documentary before?  It covers it in great details: https://www.youtube.com/watch?v=DkGR65CXaNA

Pilot incapacitation due to food poisoning does appear to have occurred.
The linked question, Is it true that the pilot and co-pilot are required to eat different meals? contains this New York Times article, which describes one incident:

In Australia in 1980, the pilot of a twin-engine commuter airliner suffered from food poisoning and collapsed at the controls. A passenger revived the unconscious pilot, who then was able to land the plane safely.

(However, this may not be quite what you're looking for, as being a single crew plane, it's unlikely he consumed the meal on-board).
The article also describes a number of near misses:

In 1975 luck may have prevented a catastrophe aboard a Japan Air Lines flight  when 143 of the 364 passengers and crew flying from Tokyo to Paris became severely ill just as the plane landed for a fuel stop at Copenhagen. They had eaten omelets that were contaminated with staphylococcal bacteria. The pilots, who had boarded in Anchorage, did not become ill because it was time for their supper, not breakfast. Instead of eating the omeletes, they chose steaks.
In 1982, 10 crew members of an Overseas National Airways DC- 8, including the pilot, co-pilot and flight engineer, became ill about 35 minutes out of Boston on a flight from Lisbon. After the plane landed safely at Logan Airport in Boston, Jo Ryan, a spokesman for the Massachusetts Port Authority, which operates Logan Airport, said, ''The crew all eat different things, but the one thing they had in common was tapioca pudding.''
In 1976 West German health officials reported that two people died and 385 others were sickened by contaminated mayonnaise served aboard a Spantax flight.
In 1976 at least 29 passengers were admitted to a hospital in Australia for treatment of gastro-enteritis after they became sick from a meal served aboard a British Airways flight from Hong Kong to Sydney.

Note the NYT article is dated 1984, so there could have been lots more incidents since then. For example, a search of the Aviation Herald for "food poison"  brings up a number. While you need to read each one and determine if the food poisoning came from the food on board, prior to the flight, or was unconfirmed as the cause, an incident of an inflight meal incapacitating the first officer occurred in a Boeing 737-800 as recently as Nov 18, 2016, flying from Spain to Denmark. In this incident, it is stated that the crew were served different meals.
It says: A chef subsequently informed the first officer that a part of her flight crew meal (cabbage stew) most likely was the source of the food poisoning. Because the cabbage grows in contact with soil, and since it most likely was only heated and not cooked during preparation, live microbiological bacteria might have been present in the hot meal.

I'd be even more scared of bacteria that weren't micro, weren't biological, or both!

Makes me want to pass up on the food service.

@mongo Just make sure you have the lasagna.

@DavidRicherby Thank you so much for that image. I'm never flying again.

@IllusiveBrian: What’s better about the lasagna? Theoretically the ground beef could be contaminated with Clostridium botulinum, whose spores can survive even 100°C boiling water temperatures …

@Michael The lasagna quip is a reference to the comedy disaster movie "Airplane," which has food borne illness as a plot element.  One of the jokes involved lasagna.

Who landed the Overseas National Airways flight if the entire flightcrew was sick?

@Sean. Reading between the lines, I think the crew were sick, but not so sick they could not remain piloting the aircraft and land. Indeed, since they did land, that must be the case.


text:
Does weather radar scare off birds?
I was told a long time ago that having the weather radar turned on when at low altitudes helps to scare birds out of your way because the can sense/feel the radar.  Casey also mentioned this in another answer of his.
Is there any evidence that weather radar actually scares off birds, or is this another "urban aviation legend"?

This has since been studies scientifically, showing evidence of weather radars affecting avian behavior. A 2015 study has seen birds notice try to get away from the radar.

(FID is Flight Initiation distance)
This wasn't unexpected; radars aren't toys. Humans can notice being exposed to low-power radars (we don't generally test on them). High-power military radars are dangerous, humans are warned not to come close, dead birds are a common sight around them. Radars have been experimented with as a less-lethal weapon against humans via their thermal effects - being cooked alive hurts.
Studies show that birds interrupt foraging behavior and start looking for threats when exposed to radars at low power. The perception is through either thermoreception or acoustic effects, like a primitive radio formed by conductive body tissues. Thermoreception would feel like eating hot pepper, acoustic effects like a sudden tinnitus. It doesn't scare off the birds per se, but it sets them into a threat-seeking mode, and they don't like birdstrikes any more than pilots do.
However, the range of this effect is <200 ft, so a weather radar can't be relied on to prevent bird strikes. It's also not well-studied and not verified across a wide range of species. The beam might also completely miss the birds due to scanning. So it's not a reliable bird deterrent. Still, it might be better to have at least some birds pay attention and possibly evade 150 ft away rather than 75 ft away. Jets are pretty quiet from the front, and it's possible, but not certain, for the radar to be noticed sooner.
This effect appears to be much more pronounced with new solid-state radars, used in airliners, than with older magnetron units used in older or smaller planes. It appears to be proportionate to mean (rather than peak) radiated power, which is higher for solid-state radars.

...at taxiing aircraft speeds (approximately 3–10 m/s) birds responding to an aircraft with the solid state radar would escape 2–6 s earlier. However, these effects may be minimized at higher speeds. For instance, approach speeds of large aircraft using solid state radars (e.g., Airbus A330) range from 62 to 73 m/s, leaving birds with 0.3 s more to escape in response to the radar.

In short: Yes, birds can feel being irradiated. They also try to avoid aircraft if they see one. This effect has a short range, so most birds might not have enough time, but keeping the radar on can slightly reduce birdstrike probability.

Birdstrikes at taxi speed??? I mean, I've heard of birdstrikes while parked  overnight (discovered an the AM preflight walkaround), but are birdstrikes while at taxi speed an actual thing in need of mitigation?

@RalphJ Probably not. Birdstrikes at takeoff and approach are though. So the study shows a small but non-zero possible effect on them. There are others, but this one is the most quantitative.

My guess is it is an urban legend. Ground based weather radar have been used track and analyse behaviour of birds. Part of this research was done with the radar in fixed beam mode to record individual wing beat frequencies for species identification, keeping the bird in the radar beam. If the birds would be scared away by the beam this research would be almost impossible (and invalid as well). Of course, that's no hard evidence that the birds aren't scared. Also the distance between the bird and radar plays a role of course.
The radar used for that research was operating in the C-band, which is also the frequency band that most aircraft weather radars operate in. Newer aircraft weather radars operate in the X-band, which is a higher frequency band. My gut feeling is that the higher frequency is even less likely to bother birds, but then again, I am not a bird so what do I know?
jwenting suggested in a comment that this myth might have been started because of incidents where animals and humans have been harmed and killed by high power radar transmissions.
The FAA has published an Advisory Circular on recommended practices and precautions for operating weather radar on the ground. While not concerned with birds, it provides an example calculations of the output power and safe distance of a weather radar. It the example, the safe distance is less than 4.5 meter. That is too close for a bird to avoid a mid air collision.

might have been started because of incidents where birds and other animals (including humans) have been killed by high power radar transmissions (one reason why you're not allowed near a transmitting high power radar antenna).

@jwenting Might be the source of the myth, but the distance at which a weather radar causes harm is too close for a bird to avoid a mid air collision. It's in the order of a couple of meters.

yes, hence the myth... Unless the radar is malfunctioning and transmitting way more energy than it's rated for (and even then you'd possibly get hit by the cadaver, suffering a dented radome as well as a lump of molten electronics).

... or some animals are more sensitive than the regulatory panel took into consideration (gasp).  Agree that likely this is a myth

Note that this answer predates 2015 and later studies, which have checked these pilot rumors and seen the birds actually react to radars, although only at 200 ft, which might still be too late.


text:
Why is the FDR and CVR put into water again after a water crash?
When a plane crashes in the water and the investigator team looks for the FDR and CVR, why do they put it in a container of water when they find it ?

This is actually a fairly standard thing to do with electronics that have been submerged: They are placed in water (ideally fresh, clean water) to both delay the onset of corrosion and dilute any salts or other chemicals that they came in contact with while submerged.
When you remove electronics from water and let them dry out they begin to form corrosion on all the little exposed bits of metal - chip legs, solder joints, capacitors, etc. - which can badly damage the device when it is powered back on.
Keeping the device submerged in water delays the onset of this corrosion because the dissolved oxygen in the water is lower than the oxygen in the air that would be hitting those parts as they dry out.
The Cockpit Voice Recorder and Flight Data Recorder are water resistant, but they are not necessarily waterproof (particularly after a crash, which may puncture their casings or damage seals), so they get placed in a container of fresh water for their trip to the NTSB's lab.
When the still-immersed equipment arrives at the NTSB laboratory it can be examined and dried in a controlled environment, maximizing the chance to recover data.

For more gory details check out The NTSB Flight Data Recorder Handbook for Aviation Accident Investigations.

Bonus Factoid: Archaeological recoveries from bodies of water use similar procedures, for similar reasons: If you bring up a clay pot that's been sitting at the bottom of a lake for a thousand years and let it air-dry naturally there's a good chance it will crack and be destroyed.
In archaeological recoveries the usual practice is to keep the item "waterlogged, ideally in waters associated with the original context" (i.e. "in a bucket of water from where you got the thing").

After being sunk in water, especially salt water, the devices are more susceptible to corrosion when removed from the water. In order to better ensure a successful recovery of the data contained within, the investigators keep them immersed in water until they can be properly cleaned and dried in a laboratory. If they were to be simply removed into the air, corrosion would begin immediately, increasing the odds of data loss.

Is that just because of the damp surfaces now being exposed to air? Otherwise, you seem to be saying that the lump of metal "knows" that it used to be in water so it somehow corrodes more quickly.

@DavidRicherby: Yes.  Corrosion (at least, the kind we're worried about here) requires both oxygen (usually, as in this case, coming from air) and water (with saltwater, such as from the sea, promoting corrosion more aggressively than fresh water; pure, distilled water is virtually noncorrosive).  Before a crash, the recorders are immersed in oxygen (from the air), but are exposed to either no or very little water (depending on the ambient humidity); hence, they corrode slowly, if at all.  After a crash into the ocean, they are immersed in saltwater, but exposed to only a little oxygen...

...(the exact amount depending on how much air is dissolved in the water), so, although they do corrode, they only do so slowly.  However, if the recorders are taken out of the water and left out of it, they will now be simultaneously wet with a still-considerable amount of saltwater (which will become much more concentrated, and, hence, more corrosive, as it evaporates) and bathed in oxygen-containing air.  Under these conditions, with ample quantities of both saltwater and oxygen, corrosion rapidly ensues.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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What can passengers do if they realise their plane is not on the right path?
In the case of flight MH370, I think passengers on board would have long enough time to realise that something is wrong with their flight. I have a habit of carrying a compass with me when I travel abroad. If the plane is not heading in the general direction towards its destination once it reaches cruising altitude, then I would be worried. This is especially so for passengers on board flight MH370 when it appears that it is flying in the opposite direction for a very long time.
What can a passenger do if he realises that the plane is not flying in the right path, i.e. a possible suicide mission or hijack?

http://en.wikipedia.org/wiki/United_Airlines_Flight_93

In the case of MH370 if the pilots were passed out, so were the pax.  Even if the masks deployed, that is only 15 minutes of O2 and you are tethered to the mask.  You aren't going to be able to do anything.

If my pocket compass contradicted expected flying path, I'd double check with the Sun's position before doing anything else - provided that the Sun, stars or any other useful reference are visible.

re: "What can a passenger do if he realises that the plane is not flying in the right path, i.e. a possible suicide mission or hijack?": Note that a deviations from the "right path" does not necessarily denote something nefarious. There are several non-nefarious reasons: adverse weather deviations, diversion to another airport (due to weather or a technical problem), flying a holding pattern pending clearance for landing, avoiding proximity with other aircraft (rare), strategic lateral offset procedure (rare), etc.

@rainbowtableturner Many of these examples would only explain a rather short term deviation from general direction to destination though.

The compass might be significantly off onboard the aircraft though.

Given the time of day that flight took off, your entering assumption comes off as misplaced.  It was nearly midnight when they took off ... most of the passengers have a reasonable chance to have been asleep, or trying to sleep. Flight 370 took off from Kuala Lumpur International Airport at 00:42 local time;  At 1:19, while Flight 370 was over the South China Sea between Malaysia and .

01:19:30 KL ACC instructs the crew to contact Ho Chi Minh ACC (HCM ACC). The aircraft passes waypoint IGARI as the captain replies, "Good night. Malaysian three seven zero." This is the final voice contact with Flight 370.

Check out the timeline here

@CptReynolds: the first 3 could, particularly the second one obviously. Note that I didn't give any timeframe.

Okay, so, going with the idea that you have a compass (and also with the idea that this can be a general question, not necessarily about flight MH370).  If you're heading from Tokyo, Japan to Seattle, Washington, USA (direct), then you could be reasonably certain the craft should be somewhere between headings 45 and 135.  So if you notice the craft is on a heading of 270 (ie., clearly you're going in the opposite direction) and this direction has been sustained for say, an hour, I'd think it would be okay to at least ask the cabin crew what's going on.
As with any time you are raising a concern with the cabin crew, you should be polite.  As has been stated, they are used to passengers being a bit nervous and, as a result, they can easily interpret belligerence as a sign of irrational fear.  And, as you might guess, it's easy to ignore someone if you feel they are being irrational.  So, if you want be taken seriously, be polite.  You're far more likely to get an actual answer, or raise a valid concern even.
So, if you just ask, "why are we headed west instead of east" they may have a very simple answer like, "well, the pilot mentioned we might have to take an odd route to avoid some weather" or "this is the flight to Bombay India, how did you get on it?"  Or, they may have no idea and be concerned themselves, so they go and ask their superior.  Thus, goal achieved, you've alerted the flight crew :).
Either way, so long as you're polite and don't become insistent (or belligerent) that you are correct, I can't see any harm in just asking.  And sometimes asking is what leads to a problem being solved so...  I'd say go for it.

I concur with others that most passengers have no clue.
I flew from Toronto to Seoul.  The flight headed northeast, paralleled the east coast of Ellsmere Island with Greenland visible off the right side, then on into the Arctic, making land over Siberia somewhere, further over Ulan Bator, across China and into Seoul.  The north pole was always in the left hand semicircle RELATIVE BEARING.  This was all due to the winds aloft on that day.  This was always visible on the plane's installed in-flight information system.  Perfectly normal flight.  To a non-experienced aviator, this would seem like a nonsensical route possibly indicating a hijack situation, and fuel a lot of worry.  Cabin crew should respond to questions of course, but in most cases there is no cause to worry. So I too have a concern that a passenger having convinced him/herself that the plane is off course will do something to jeopardize the safety of the plane, crew, and passengers.

Bear in mind that many long-haul passenger flights have moving-map systems that show the passengers the flight's position and progress.  Whilst I personally don't carry a compass (and even if I did, would be very unlikely to check it when flying as a passenger), I would almost certainly notice if we were heading the wrong direction for any significant period of time.  I would likely assume we were having to divert and seek to confirm with cabin crew; any subsequent action would depend upon their response.

@eggyal:  On a transpolar flight, how is the user of a magnetic compass to know in which direction Magnetic North should be?  Magnetic compasses are very misleading to the layperson in the polar regions.

I agree that most passengers have no clue, but that doesn't mean all passengers have no clue. If I were on that Toronto-Seoul flight and I saw that we were flying towards Washington, D.C., I'd definitely ask the flight crew what's going on. I'd also wave at the NORAD escorts. - lol

Not only do most people have no clue about that direction they're supposed to be flying, the number of people alerting the crew of "wrong directions" from those that do and get nervous when the plane diverts to avoid a thunderstorm or simply switches to another airway that diverts from the direct course would quickly make the crew ignore any and all such comments from passengers.
Which is no doubt one of the reasons they don't like passengers using handheld GPS devices (quite apart from the blanket ban on anything that has an antenna).

"Which is no doubt one of the reasons they don't like passengers using handheld GPS devices (quite apart from the blanket ban on anything that has an antenna)."
Where is such a ban in place? Certainly not in the U.S. They're not even banned under 10,000 ft. anymore in the U.S. I've used the GPS on my phone on board an aircraft numerous times. No one cared. It should be noted that GPS receivers are just that - receivers. They don't transmit anything, so they were never banned along with transmitting devices like cell phones and wifi.

@reirab: here is a list (as of 2010) categorizing airlines on whether or not they allow the use of GPS receivers in flight: http://gpsinformation.net/airgps/airgps.htm

@JacobKrall Hmm... Interesting link, but it seems a bit dated. Many of the airlines on those lists don't even still exist. I'm especially surprised to see Northwest on there, since Delta bought them 7 years ago and even their brand name hasn't existed for over 5 years now. I suspect that the rise in smartphone usage (nearly all of which are GPS capable, at least in the case of the ones sold in the U.S. market,) almost any airline would allow it nowadays and most wouldn't know the difference even if they didn't allow it. A lot of them even show you the flight's position and velocity on the IFE.


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Could a pilot incapacitate other crew/passengers by manipulating cabin air quality/pressure?
Could a pilot of an airliner incapacitate everyone outside the cockpit by somehow triggering a loss of cabin pressure while simultaneously disarming the airplane's oxygen masks, manipulating the air circulation system to induce hypoxia, or some other means?
For example, would it be a credible theory that the pilot de-pressurized the 777 flying Malaysia Airlines Flight 370 and flew it off somewhere?

I think that you question is kind of irrelevant with todays hardened cockpit doors.  Even if the passengers were aware of what was going on (and unless there was some kind of flight tracking displays in the back they very well might not be), they still can't get into the cockpit.

@Lnafziger- Right, but if you had trained crew locked out of the cockpit for that long, would there not be a way for them to signal distress somehow?

Well, your question is "Could a pilot of...." so I am assuming that the trained crew is still in the cockpit, not locked outside of it.  :)

@Lnafziger - no, the scenario im putting forth is a sole operator, either one of orig pilots or another, commandeering the cockpit and incapacitating others on board, including rest of crew.

Well, what I am saying is that the "seemingly executed without resistance" bit...  If the pilot is locked away in the secure cockpit, there isn't much that anybody in the back can do.  Since the pilot shut off the communication equipment they could also have shut off the satellite phones that are in the back.  There's no way for people in the back to communicate unless the airplane flew low enough for cell phones to work.

@Lnafziger- That answers another question I had- whether communication would still be possible from outside the cockpit..

What would happen if the forward switch was on but the aft switch was accidentally left closed?

The answer depends on what kind of aircraft you're talking about, and how much control the crew has over the pressurization systems.
For example, in theory you could very well reduce or completely shut off the air to the cabin on a 777. This could also be done by a single crew member alone. The pilots have full control of this system should say the one of the engines produce bad air to that cabin and would needed to be switched off.
As for the oxygen masks- these are for emergency descent use and have a generator that runs out after about 15 minutes. The crew bottles last a bit longer I think, but these will also have a limit, and doing any attempt to break through the bullet-proof cockpit door in those conditions I'd imagine would be very difficult, since I'm not sure you're still picking up the amount of oxygen you normally would.
For a similar situation (though not a deliberate attempt) you can read up on Helios Airways Flight 522.
For an idea of how the pilot masks look, see this video.
Source: SmartCockpit

@Manfred- Yes the Helios crash is what got me thinking about this. But in this case would the pilot have a way of maintaining cockpit pressure so they wouldn't pass out themselves?

cockpit pressure is equal to cabin I believe, and it may be that the pilot supply lasts longer than the passenger's supply

@Yarin if it was an act of a single crew member he'd also have access to the ration of three crew members, further prolonging his advantage.

There is the issue though of altitude decompression sickness, especially with prolonged exposure to these conditions if they have not breathed 100% oxygen throughout the flight: http://clusterballoon.com/assets/Chamber_FAA_AltitudeDecompressionSickness.pdf

And if the pilot really did climb to 45000 feet as reported, he would only need to depressurize temporarily, as it would have quickly been lethal to those without extended oxygen supplies

@Manfred any guess as to how fast depressurization would happen once air were manually shut off?

@Yarin not a clue, but i'd think it would take a few minutes, but that's just a guess.

@Yarin: They don't need one - they can simply don their oxygen mask (which has many hours' worth of oxygen available, far more than the ~15 minutes or so, at most, that the passengers have access to).

Yes, I think it would be very easy for the pilot in command of a 777 to do this — here's one scenario:

Ask the copilot to get a glass of water and lock the cockpit door behind him
Don and activate the oxygen mask
Close the engine bleed air valves that supply cabin pressure
Open the controlled outflow valves to equalize cabin pressure to altitude pressure
Put the passenger/supernumerary oxygen to "reset" (or pull the circuit breaker)
Ascend a little bit above the service ceiling of FL 410.

At FL 450, consciousness is measured in seconds, death in about 4 or 5 minutes.

I read somewhere that Flight 370 flew at FL 450 for 45 minutes.  I wonder if it is coincidence that the 3 flight O2 supplies 15 minutes each? 3 X 15 = 45?

Very simple operation and you don't need to be at 41,000 feet to do it. Anything above about 21,000 feet and you die in a few minutes; you just fall asleep.
If you are really paying attention, you would first notice your fingernails (under them) will turn blue due to a lack of oxygen first. A few giggles perhaps, then you'd pass out and DIE. Quite painlessly actually.

Death at 21000 ft will take hours

The answer is yes: if one of the pilots needed to use the restroom, regulations require the other pilot to put on his O2 mask while the other pilot is away. Once outside the cockpit, the other pilot could lock the door and the other pilot out. Then he could turn everything off.
Also since it was at about 1:30am, most passengers would be trying to sleep in their chairs; additionally the masks that drop only have enough O2 to last while the aircraft descends to a lower/safer altitude — so if the plane maintained altitude, there would only be 5-10 minutes of O2 and everyone would pass out and eventually die.
Unless it landed on smooth water, like the miracle on the Hudson, the plane's ELT (Emergency Locator Transmitter) would go off and the crash site would be pinpointed by satellites within seconds.
So therefore one of two things happened:

It landed on water softly and is now at bottom of ocean, or;
It landed safely on land because there was no ELT signal.

Yea interesting that practically no one's talking about the ELT, but it failed on Air France 447, so not clear how reliable they are in water crashes.

Ever since the LAM470 incident, it has been required that two crew members be in the cockpit at all times specifically to prevent a one pilot locking the other out like this.

re: "regulations require the other pilot to put on his O2 mask while the other pilot is away" can you provide a reference for that ?

This answer would be much better without the speculation at the end.

Depressurization leads not only to the lack of oxygen in the cabin (and cockpit), but likewise may lead to a dramatic drop in temperature.
For altitudes above 38,000 - 65,000 feet, the outside temperature is roughly -70°F/-55°C.  Combined with data suggesting that at 40,000 feet a passenger sitting quietly would retain consciousness for only about 18 seconds with the loss of oxygen from depressurization (and thus presumably fewer seconds at 45,000 feet), it may only be a matter of seconds, not minutes, before everyone in the cabin would be dead.
What I don't know and wish I did know is whether the cabin and cockpit have separate pressurization systems.  I assume so.  This would make it even easier for a pilot to incapacitate/kill all crew and passengers.


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Flight path question? re missing 777 MH370
Can someone explain why the aircraft would fly in an arc using the satellite as a reference point? Have I missed something?

it didn't fly in an arc, when the plane pinged the satellite they can get the distance between the plane and satellite, which means that the possible locations of the plane is on an arc centered around the satellite. If they had another reference point they could be surer of where the plane is

yes, you missed lots of things. Although nobody knows for sure what happened, some people were able to use data captured by the sat to try to guess were the plane went.

See http://aviation.stackexchange.com/q/2623/1289 and http://aviation.stackexchange.com/q/2472/1289

thank you RedGrittyBrick, the only reports I had seen suggested all 6 pings fell on that arc, not just the last one. It seems we can't be trusted with too much info

@user2109 It's more likely that the reports suggesting all pings were on the arc were simply incorrect...

@user2109: I attribute this to "Chinese whispers": The scientists tell their manager, who dumbs it down for the executive, who sends it to his counterpart in the S&R team, who translates it to Malaysian, then simplifies it for PR, who reword it for the press, then translate the result into English for the non Malaysian press, who read it to reporters, who send their jottings to journalists, who write an article dumbed down for their readers, which their editor edits, which you read. Somewhere the word "corridor" got chosen and someone wrongly inferred that people travel along corridors.


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What is the procedure if both pilots are incapacitated?
Let's say both pilots passed out , is there anyone else from cabin crew that is trained enough to land a plane?

I wonder the possibility that this happened to MH370.

While there is no recorded incident of this ever happening for large airliners, there is the possibility of what is often known as "talk down aircraft landing" where someone is instructed over radio, however this is not part of any official procedures. There is the possibility to do training courses in some simulator facilities for exactly those things, though I have never heard of any airline doing this officially for their crew.

See Helios Flight 522 for an example of this happening on an airliner. Unfortunately it was not a good outcome.

@Dezza wow , thanks for the example

Related: Can a passenger realistically replace suddenly incapacitated pilots?

Also related: How do commercial airlines prepare for pilots falling sick during the flight?

To put it short: no.
Unfortunately it might even take a while for anyone to notice both pilots are out. Most likely the first would be an air traffic controller since he/she couldn't reach the pilots on radio.
If the cabin attendants find both pilots incapacitated, they would most likely

try to find a doctor or nurse to help recover a pilot
try to find if any of the passengers was a pilot

It seems to me that a bigger problem might be access to the cockpit. Can the cabin crew open the cockpit door without the cooperation of the flight crew?

@dlu sorry, can't comment on that.

as in "don't know" or as in "you could tell us, but then you'd have to kill us." :-)

@dlu more the latter, not so strongly though :D

Whew, glad to hear that :-)


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What happens when a pilot is incapacitated?
Is there a contingency for such a situation, where one of the pilots leaves the cockpit, the other pilot is incapacitated (for example losing consciousness) while the first pilot is still outside the cockpit and can not reenter the cockpit. If there is not, is that not a huge flaw, as multiple pilots are meant as a redundancy.
Edit: This is in my opinion not a duplicate of this question, since the big problem in my question is the door to the cockpit being only openable from the outside.
In the linked question, the answer is simply "both pilots being incapacitated at the same time is highly unlikely". The scenario I described is not highly unlikely. One of two pilots being incapacitated is not improbable and the door to the cockpit is only openable from the inside.
So if one pilot is incapacitated while being temporarily alone in the cockpit, the other pilot is "automatically" locked out of the cockpit.

What makes you think the door only opens from the inside?

the door can be opened from the outside: http://aviation.stackexchange.com/questions/2803

@SentryRaven: This article in the NY Times states that “But what is sure is that at the very end of the flight, the other pilot is alone and does not open the door.”

the NYT is speculating, that's not official information.

See the question referenced by @Federico above. The cockpit door can be opened from both sides, there is an override function that will deny the entry attempt by code from inside however. Until a reliable source, such as the French BEA or another investigating party reports the contents of the CVR, everything else is still speculation. The NY Times is not a reliable source in my books.

Okay, both other questions taken together answer my question sufficiently. I want to point out that I did not mean to ask specifically about flight 4U9525, but about the general scenario.

Isn't there a rule (airline, FAA, etc?) that if a pilot leaves the cockpit another crew member must enter the cockpit so that there are always two people in the cockpit?

@RedGrittyBrick That is something I wanted to know about, hence the question.

but that's a different question.

@Federico: Arguably it's a part of (to paraphrase the Q) the "contingency for PF incapacitation while PNF is outside cockpit" - I'm adding an answer on that basis. :-)

@RedGrittyBrick you can edit the question to make it more unique and it will be reopened

There are contingency measures for PF incapacitation when PNF is absent from the cockpit.
This includes measures for cockpit decompression (e.g. window breaking)
These measures are balanced with measures to prevent unauthorised passengers forcing entry to the cockpit, including by using force on cabin crew (or PNF) to make them open the cockpit door. Some of these measures are at the airline's discretion.
Cockpit door locks
According to The Guardian Newspaper

A locked door is opened by a flight crew inside the cockpit but can also be unlocked by cabin crew entering a keycode from the outside. Crew inside the cockpit can manually override it to keep a door locked for up to five minutes.
“In the case of an electrical supply failure the door is automatically unlocked, but remains closed,” reads the manual.
It is equipped with a manual escape hatch but that is only accessible from the inside.

According to The LA Times newspaper

safety protocols mandated by Congress in the U.S. after the Sept. 11 attacks ... eliminate the use of keys for entering the cockpit - assuring that no errant passenger can wrestle a key away from a crew member. ...
If a member of the flight crew doesn't open the locked cockpit door from the inside, according to a manual for the Airbus A320 available online, the door can also be unlocked by the cabin crew outside the cockpit by entering a two- to seven-digit code, pre-programmed by the airline, on a keypad.

Cockpit occupancy
Guardian:

Protocols and standard procedures around what happens when a pilot leaves the cockpit mid-flight vary according to country and airline.
A flight attendant taking the seat of an absent pilot to ensure there are always two people in the cockpit, and/or blocking access to the open door with a trolley, are often seen on US flights, but not necessarily on others, [Aviation expert Neil Handsford] said. For instance it is not a requirement on Australian flights.

LA Times:

American experts say the typical procedure is for a flight attendant to use a food cart to block access to the cockpit when the pilot opens the door to leave. A flight attendant is supposed to remain in the cockpit and open the door for the pilot upon his or her return. ...

Airbus Manual
The Airbus manual referred to above says

The Cockpit Door Locking System (CDLS) provides a means of electrically
locking and unlocking the cockpit door. This system is mainly
composed of :

A keypad, located in the forward cabin, near the cockpit door,
A toggle switch, located in the center pedestal’s Cockpit Door panel,
A control unit and its CKPT DOOR CONT normal panel, located on
the overhead panel,
A buzzer.

The keypad enables
the cabin crew to request access to the cockpit. There are two
different access request types : “Routine” and “Emergency” access
request (Refer to PRO-SUP-25 Cockpit Door Operation - General).
The
toggle switch enables the flight crew to lock or unlock the cockpit
door, following an access request, thereby allowing or denying the
entry to the cockpit.
The cockpit door control unit is the system controller, in charge of :

Locking or unlocking the door latches, upon flight crew action.
Unlocking the door, in case of cockpit decompression
(the door then opens towards the cockpit under differential pressure).
Indicating system failures of electrical latches and pressure sensors.
Activating the access request buzzer and turning on the keypad LEDs.

The buzzer sounds in the cockpit for 1 to 9 s to indicate that
a routine access request has been made, or sounds continuously if an
emergency access procedure has been initiated.
The keypad is used to sound the buzzer in the cockpit for 1 to 9 s (3 s by default), by entering a zero to seven-digit code, as programmed by the airline, followed by the '#' key. It is also used to enter the two to seven-digit emergency code, followed by the '#' key, when the flight crew does not respond.

There is also an Airbus Video that shows how the cockpit door lock operates normally and in the case of pilot incapacitation

Abbreviations
PF = Pilot flying, PNF = Pilot not flying.

Is there a contingency for such a situation, where one of the pilots leaves the cockpit, the other pilot is incapacitated (for example losing consciousness) while the first pilot is still outside the cockpit and can not reenter the cockpit.

Yes, a keypad on the door will allow the second pilot back into the cockpit. It doesn't help when the pilot outside doesn't know/forgets the code or if the unlock code is denied from inside the cockpit.


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How tight should passengers wear the seat belt?
How tight should a passenger wear the seat belt?
During takeoff and landing and other moments the seat belt sign is on, I usually pull the belt as tight as possible. This is little uncomfortable, so I loosen it a bit when the seat belt sign is off. I think that one or maybe two fingers might fit between the seat belt and my body.
Is this a good idea? Would wearing the belt as tight as possible give a greater risk of crushing my pelvis bone or something?
Please specify whether there is a difference between a situation where the seat belt sign is on and a situation where the sign is off.

According to this document published by the FAA (about smaller GA planes but the topic is applicable)

Tests have shown that slack in the restraint system should be minimal.
  In an impact, your body keeps moving until the slack is taken out of
  the restraint, but then must be abruptly stopped to “catch up” with
  the airplane. The restraint should be adjusted as tightly as your
  comfort will permit to minimize potential injuries.

Here is a video of them testing the seats. You can see the waist lines of the dummies does not move very much.
Here is an interesting research paper on the topic, may be worth checking out.
A study was conducted by the DOT "Human Factors Associated With the Certification of Airplane Passenger Seats: Seat Belt Adjustment and Release" on the difference between belt tension (as applied by a passenger) in both a cruise and emergency setting. This looks like the most conclusive numbers I can find on measured tension.

An analysis of results indicate that most passengers (90%) tighten
  the lap belt to a tension less than 7 lb. during normal flight
  conditions and less than 10 lb. for an anticipated emergency.

Great answer, but I would like to offer a brief translation, "make it snug."


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Is there anywhere one can buy or find plans to build a human powered aircraft?
I was surprised to find that only two Gossamer Albatrosses were built. Is there any way to get or build an aircraft like that today? (I don't mean design your own).

@mins As small as possible? Let's say  $20,000.

According to this article crossing the English Channel with the Albatross may have costed $200,000. For 3 hours and 40 km. This figure may be inaccurate and include event-related costs, but this gives an idea.

@mins  I think that includes much more than just the cost of the plane. But more importantly, materials may have gotten cheaper and much of the cost of the plane must have gone into the engineering behind it, not just the raw materials.

Yes, contact Todd Reichert, PhD, or Cameron Robertson at Aerovelo Inc.   They have designed, built, and demonstrated the first human powered vertical aircraft at the University of Toronto, of which they are alumni, and they won the Sikorsky prize of $250,000 for it.
They have aero-velomobiles that can smoke the albatross.
Note: The ability to get airborne in these Ultralights is heavily dependent on the weight and athletic ability of the human operator.

I didn't mean human powered helicopter. I was wondering if there was any reasonable way to get something like the Albatross or one of its successors.

For 20,000 USD You can paraglide on a good day and not need any power except for that of Thermals and wind.
If you really want to have something human powered, then after the chute costs, you can attempt a pedal-based propellor. all chute equipment will run ya about 5,000-10,000 USD, depending on the source, leaving more than half available for constructing your strange propellor.
That said, I highly doubt that any useful thrust will come of it; it'll weigh more than it's worth.
The sad truth about human power is that it's not very good. It's so bad in fact, that it's not worth using in any aviation-related practicality.

Plans for Gossamer Albatross and Daedalus are available if you search for them online. But skills required to build a usable aircraft require some talent and great patience. Depending where you live, materials can be pricey.
Personal experience:
I have been working on my own HPA design for >25 years (yes).
I have found that the successful builders are often happy to give you pointers - so find out who they are, and try email them! (I am not going to cause them spam by listing emails & names!)
Building such a plane (on your own?) is an intense labour of love - fraught with great obstacles. It will require great tenacity and an ability to withstand ridicule and disinterest from friends and family.
Easy flier (Daedalus), plans are out there, just google...
Speed and maneuverability (Musculair), You may be able to find the plans...
Those were the very best (real working examples), so far.
There is yet to be be a practical HPA for sport and recreation.
Prizes for one who succeeds!


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Why are oxygen requirements based on pressure altitude?
The FAA's oxygen rules in §91.211 are based on pressure altitude. Assuming our lungs are like our engines and wings and dependent on density altitude, why are the oxygen requirements not based on density altitude?
If the answer is practicality, then would it not be wise to be more conservative with these requirements on hot days and more lenient on cold days?
Living in Colorado, the oxygen requirements are almost exactly what is usually required to transit the front range of the Rockies without an oxygen bottle, which leads me to believe practicality played a part. If density altitude were used instead, on a hot day you'd be unlikely to remain within the regulations and still transit the area without hitting anything made of rocks.

Our lungs take in oxygen based on partial pressure: How do people suffering from hypoxia not realize they aren't getting enough oxygen?

I believe partial pressure is dependent on density altitude, not pressure altitude.

@John, partial pressure is dependent on pressure altitude. That should be rather obvious since the partial pressure is just the total pressure times volume fraction of given compound. Temperature would only come into play if the thermal expansion of each compound was significantly different, but they are not.

Jan, I think the FAA has confused us by suggesting a redefinition of the term "pressure". Partial pressure is computed as you say, but the pressure you mention includes temperature. Pressure altitude also includes temperature, but it's at a temperature defined in the ISA, not the actual temperature.

I gotta believe that part of the reason is because airplanes file flight plans for a pressure altitude, and the altimeter reads pressure altitude.  Do you really want to be calculating density altitude enroute to determine compliance and possibly squeeze just a little bit more out of the regs?  KISS applies here...

The air in the lungs is in pressure equilibrium with the cabin, but not temperature equilibrium. It's always at body temperature. So the only variable that can affect how much oxygen is available to the body is the pressure of the outside air - thus pressure altitude, not density altitude, is physiologically relevant.
That said, if the density altitude is high it may mean you are hot and dehydrated, and the deleterious effects of those factors may be additive with those of hypoxia.

Even more importantly, the limiting factor is adsorption of oxygen on the hemoglobin and that process is governed by partial pressure.

I believe both pressure altitude and partial pressure necessarily must include a temperature, it's just not the one that's actually outside or in our lungs when using the ISA temp. So I think this answer could be restated: The temperature outside (and therefore density altitude) is not relevant because our lungs always heat or cool air to body temperature. This would still mean pressure altitude is not accurate as the ISA temp used in pressure altitude is usually not body temperature. https://en.wikipedia.org/wiki/Barometric_formula#Pressure_equations

Assuming our lungs are like our engines

They are not. Engine (at least spark-ignited reciprocating one) uses most oxygen in each charge and its RPM is limited, so it can't be run faster to compensate for the lower air density.
However, our bodies only use small fraction of oxygen from each breath and we normally breathe much slower than we can if need be.

and wings

They are not. Wings depend on dynamic pressure, but dynamic pressure is not involved in any significant process in the lungs.

and dependent on density altitude

Well, they don't. The limiting factor for respiration is the rate of association of oxygen to the hemoglobin. That depends primarily on partial pressure of oxygen and since partial pressure is just pressure times volume fraction, on pressure altitude, not density one.
Temperature does affect the association rate, but since the temperature is that of blood, and we are warm-blooded, the temperature is fairly constant. And the effect is different from that on density anyway.

There are many other factors that affect the association rate that are physiological and have nothing to do with the weather and everything to do with the person.
Therefore there must be safety margin built into the rules. I can offer two anecdotes:

When I went up to 14,000 ft, we spent several days around 12,500 ft. Still, just around 14,000 ft, one of the 16 people there got, rather suddenly, symptoms of altitude sickness and had to turn back immediately. While the rest, most were fine and few (including me) were not able to exert much effort, but were otherwise also fine.
Note that this shows the safety margin is not all that big. For some people, 14,000 ft is dangerous, though for most it is not.
During WWII, US Army was supplying China via airlift over Himalayas and the route had minimum safe altitude of 19,000 ft. They had some strange accidents where the aircraft failed to round out after apparently normal approach and crashed at the threshold that happened mainly on the Chinese side where airfields were around 7,000 ft (while they were almost sea level on the Indian side). Investigation showed that apparently some pilots didn't use oxygen. Obviously they didn't feel unwell, but the reduction in mental performance showed. Strict order to wear the masks did resolve the issue, proving the analysis [1].

[1]: Tunner, Lt. Gen. William H. (1955). Over the Hump; unfortunately the link on WP is dead, so I am linking the WP citation in the hope somebody will manage to fix it.


text:
Why does IAS decrease with lower air density if power is constant?
TAS increases with less dense air, which is intuitive. What I don't understand is why IAS decreases.
This is assuming sub-transonic speeds where compressibility effects are negligible.
To phrase this in more practical terms, if you look at the climb table in a POH for a turbocharged airplane you will see full throttle climb rate drops with an increase in altitude/temp, even before the MP drops. EAS and propeller efficiency would not seem sufficient to explain the IAS drop seen.
I would think that given a TAS, pressure altitude, and temperature, one could derive the IAS but I have not seen any math to do this.
This is in reference to a turbocharged propeller driven airplane that is capable of maintaining power at higher altitudes.

My current guess is that this is related to less aerodynamic efficiency at higher altitudes, as described in the AFH, but that’s basically where it ends. I’m interested in why this occurs and to what extent.

Because even with constant power, thrust decreases with velocity, also known as TAS.
Drag depends mainly on the dynamic pressure, which is what IAS represents, so if you had the same thrust, you'd have the same IAS too.
However a piston engine produces approximately constant power (if your RPM is in the optimal range), and power is thrust times velocity. So the turbocharger lets you have the same power in the less dense air, but because your true airspeed is higher, the thrust is a bit lower and therefore your (maximum attainable) indicated airspeed is as well.
And then there is the effect of RPM. Engine power (of any engine) is limited by RPM, growing up to some optimal speed and then declining (and then you get to the red line). If you have a fixed propeller, your available power grows with speed first as the RPM increases with decreasing effective pitch, but then you cross the optimum and the power starts reducing and then you hit the red line and have to retard the throttle. And effective pitch again depends on TAS.

IAS drops significantly in actual airplanes with the same percentage power setting.  It could be that lower is constant while thrust drops so I have updated the question.

@John, thrust drops even for constant power, but in most aircraft you also don't get the same power with the same throttle setting. To get constant power you need to maintain constant manifold pressure, but that usually means gradually moving the power lever forward.

My question is why thrust and/or drag changes with changing air density given constant power, rather than if it occurs (it is known it does). Only simplistic explanations seem to be available ("it's just less efficient," etc.).

@John, and I have already answered that question as best as I could. Drag (which is force), depends on EAS (IAS), but for the same power, thrust is inversely proportional to TAS, so you have less of it at the same IAS.

Jan, thank you. Do you have any more information on why thrust decreases with velocity given equal power? This would seem to be the reverse of how some engines (ex: ramjets) operate. Is this related specifically to propellers? Since the airfoil on the wing seems roughly as efficient, or at least the AOA is the same, this seems counterintuitive to me.

@John, that's basically by definition. Power is energy per time ($P=\frac{\Delta E}{\Delta t}$) and work (energy) is force times distance ($\Delta E = W = F\cdot \Delta s$). Substituting velocity as distance per time ($v = \frac{\Delta s}{\Delta t}$) you get that power is force times velocity ($P = \frac{\Delta E}{\Delta t} = \frac{F\cdot\Delta s}{\Delta t} = F\frac{\Delta s}{\Delta t} = F\cdot v$). Jet engines use the ram pressure to increase their pressure ratio and therefore their thermodynamic efficiency and power, but that only works at transsonic and higher speeds.


text:
Why is IGN SYSTEM A FAULT dispatch a NO GO on the A320 for ETOPS?
In the A320 MEL if Ignition system A is under MEL the aircraft can't be dispatched for ETOPS. Why is it specifically restricted for ETOPS because even while conducting non ETOPS
 if we go into emergency electrical configuration we will still lose ignition system A.

Your assumption is incorrect.
In ELEC EMER CONFIG (see your QRH - ELEC EMER CONFIG SYS REMAINING), Ignition A is the only ignition available and hence that would be your reason why IGN A is needed for EDTO / ETOPS.

this is not my assumption but mentioned in the official MEL document of my company.


text:
If ELAC 1 is under MEL why is it a NO GO item when carrying out EDTO on the A320?
In the MEL for the A320 it is mentioned that ELAC 1 is a NO GO if carrying out EDTO operations. Why is ELAC 1 specifically for EDTO? In that case shouldn't it be for non EDTO operations also.
This somewhat contradicts ELAC 2 being a NO GO. Could someone please clarify this with an official reference.

For those of us not embroiled in A320 operations: ELAC - ELevator Aileron Computer, and EDTO - Extended Diversion Time Operations

@ymb1 didn't mean to pertain specifically to the A320. But while conducting EDTO on the A320.

Basically, operating ETOPS/EDTO takes into consideration worst-case scenario situations (EMER ELEC CONFIG) where you will only have ELAC1 working.
In addition, its mentioned that ELAC2 in MEL is a NO-GO item due to the logic behind the system operation where it will allow ELAC2 to work first always, and in case ELAC2 fails ELAC1 will take over.
According to :

A320 FCOM ATA (27-10-20) Architecture (Pitch control). In normal operations, ELAC2 controls the elevator and the horizontal stabilizer, if a failure occurs in ELAC2 the system shifts pitch control to ELAC1.
A320 QRH ABN-18 ELEC (ELEC EMER CONFIG SYS REMAINING), In the emergency electric configuration the ELAC2 wouldn't be available when the emergency generator is running and ELAC1 will be the only available.
A320 FCOM ABN PRO (ELEC EMER CONFIG), ELAC2 is written within the INOP SYS table to confirm what happens when the aircraft goes into the emergency electric configuration.

I couldn't still fully understand from your answer why it's a NO GO

An item may be on the MEL be sure being into for a flight, day ,or other period is an acceptable risk but when giving that approval the authorities always consider the " next worst failure" which most often is the second version of the " failed "item. It was judged that the pilot workload, or reduction on safety margins , when under Erops ( I'm a traditionalist) and potentially up to  3 hours or more from a laudable airfield.
As a general eules, far fewer items are on an erops aircraft rather than an Aircraft released for "normal" service, which assumes a diversion airfield within one hour. (The last MMEL I negotiated was parts of the Airbus A400M avionics, 8 ish years ago)

David, I realize that perhaps English isn't your first language, but please get some help editing your basic grammar.  That first sentence especially makes no sense at all.


text:
Why doesn't the autobrakes and ground spoilers deploy on the A320 if the speed is below 72 knots?
I really can't understand the reason as to why Airbus has put a speed restriction of 72 knots for the activation of autobrakes and deployment of ground spoilers. Could someone explain why this has been imposed?

Not a definite answer: I imagine someone backtracking on a long 4000 m runway might actually taxi at around 71kts?
If armed, MAX braking will occur once the system detects that ground spoilers are deployed.
From the FCOM, ground spoilers:

If the ground spoilers are armed and the speed exceeds 72 kt, the ground spoilers will automatically extend as soon as both thrust levers are reset to idle.

Because of Airbus SOPs by the time you enter the active rwy, your autobrakes are on MAX and spoilers armed. Once armed&active, they will deploy the second the ADIRS will sense any deceleration. With thr lvl retarded to idle, the plane now thinks you are actually rejecting a take off, not knowing you are slowing down at the end of the runway for the 180deg turn to lineup. All hell will break loose as your plane insta-handbrakes on the spot with the activation of spoilers+max brakes.
Incidentally, my company used to have a 30kts speed limit for backtrack which has been recently removed.

Are they armed in takeoff config? Is that in case of rejected t/o?

exactly, they are part of T/O ecam memo (done during taxi) and thus active by the time you reach the runway. Any deceleration after reaching 72kts and the  plane thinks you are rejecting the takeoff

uhm yes.. (IIUC) question was why autobrake max and auto spoiler extension is not active if plane never reaches 72kts. My (attempted) answer was: to prevent a wrongfull deployment after taxiing at high speed. I need to stop posting late at night...


text:
How does the flap configuration affect the tailstrike limit on the A320 aircraft family?
The configuration that provides the maximum FLEX temperature varies with the runway length.
On short runways, CONF 3 usually provides the highest FLEX temperature, and the tail clearance at lift off does not depends on the configuration.
On medium or long runways, the second segment limitation becomes the limiting factor, and CONF 2 or CONF 1+F becomes the optimum configuration, in term of FLEX temperature.
In these cases, the tail clearance at lift off depends on the configuration. The highest flap configuration gives the highest tailstrike margin.
How does the flap configuration affect the tailstrike limit?

It would be better to explicitly state the aircraft type in the main body of the question rather than a tag.

A higher configuration number indicates that the flaps/slats are extended by an higher amount.
In turns this means that for the same angle of attack the wings will produce higher lift (and drag) in the higher configuration.
You achieve take-off when the lift is at least equal to the weight of the aircraft, and with higher flap/slat deflection you will have sufficient lift even when the nose is relatively low on the horizon, leaving plenty of margin against a tailstrike.
On the other hand, if you are using a low configuration, the flaps/slats will be mostly retracted, and you will need a higher AoA to produce sufficient lift, meaning that you have to raise the nose of the aircraft more, leaving less margin against a tailstrike.

In order to take off and subsequently climb, the aircraft needs to create lift greater than weight. It does so by rotating.
Image source
Compare the lift of the plain airfoil with that of the airfoil with flaps: the green line produces a certain lift at a lower AoA than the blue line. It needs to rotate less in order to take off. The highest risk of tailstrike occurs at the highest rotation angle, which is required at the lowest flap setting.


text:
How does aspect ratio affect the stalling angle of the wing?
I have been trying to find a clear answer for this but haven't been able to do so. From what I understand this is linked to induced drag but I'm not able to link it.
Could someone shed some light on this ?

What are your conditions of comparison? For example, are you assuming constant wing area?

Nothing depends on aspect ratio, actually. Some properties depend on span, some on chord and some on area. And in case of stalling angle of attack it is mainly chord. I was pretty sure it was discussed at length already. This answer is relevant, but I thought there was something better I can't find now.

@JanHudec I had a hard time to find anything on stalling angles; most literature is obsessed with lift curve slope. I don't think there is an answer that covers this aspect authoritatively. The best you will be able to find is some cursory remark without proof.

Any finite span wing creates a wingtip vortex which causes an induced downwash profile that is maximum at the wingtips, and gets less as you move further inboard (towards the wing root). This is due to the vorticity causing a upwashing outboard of the wing tip, and a downwash inboard of the wing tip. If we took a theoretical wing where the aspect ratio is high enough that the span is 'near-infinite', there will be no tip-effect (vortex) induced downwash at the center (root).
Lower aspect ratio means that there is more induced downwash further inboard, and this local downwash actually helps to keep the airflow attached becuase the local flow is already flowing downwards along the later surface of the wing. You can also think of it as reducing the local incidence angle because the air is already flowing downwards.
Most wings are designed to stall first at the wing root, and for rectangular wings this is inherit due to the downwashing profile described above. For other wing shapes, designers will include "wash-out" to ensure that the root stalls first (Why does a rectangular wing stall first at the root?). Because the root is separated first, if we take away the section of the wing near the root (hence decreasing aspect ratio), the area that would have already separated is now removed, and the wing will be able to operate at a higher angle of attack.
Therefore the stall angle would increase if aspect ratio is decreased (ceteris paribus!). This is assuming that the wing is operating in the longitudinal plane only. Any asymmetrical movement (rolling and yawing), will mean that the wing could possibly stall at the tip.

I couldn't fully understand your answer. Is it possible if you could provide some further clarity to it?

I don't think it is really correct. A simple wing will stall at the tips first, leading to the opposite answer. The fact that designers sometimes massage the profile is not really relevant.

@Jai updated with more detail, anything need clarification?

@GuyInchbald a simple rectangular wing will always stall at the root first. See this answer: https://aviation.stackexchange.com/a/55213/51810. For more exotic shapes (twist and sweep), that effect is lost, and it is up to the designer to add washout back in to counteract it.

@StuartBuckingham Is your simple the same as my simple? The answer is not so simple.

@GuyInchbald please provide more context. The effect of delayed stall due to vortex effects on the outboard section of the wing is well understood. I have never seen any evidence indicating the contrary in symmetric flight.

@StuartBuckingham Ask the Shuttleworth folk how their DH.88 Comet behaves in a stall, then. Seriously, "dropping a wing" sharply following tip stall is a well known characteristic of a great many aircraft. If you need to know more, ask a new question about it.

That is not a simple wing. For a constant section wing, it will stall furthest away from the tip first.

@GuyInchbald With a straight non-tapered wing, the lift distribution is highest at wing root, that's why it starts there first. With taper, the highest local distribution shifts to mid/outer wing, hence leading to tip stall.

@JZYL Indeed. As I already said to Stuart, tho' neither he nor you seems to have noticed, "Is your simple the same as my simple? The answer is not so simple. ... If you need to know more, ask a new question about it."

@JZYL interesting approach to it - higher loading = lower stall margin. I usually look at it as the tip effect on the local flow field, and how it "supports" the pressure recovery (plus the loss in peak suction), but you're just as correct.

"At an infinite wingspan there will be no downwash at the root"? Perhaps not from the vortex, but some from the airflow off the bottom of the wing (at positive AOA).

@RobertDiGiovanni - Correct. Answer updated

The basic principle is that most subsonic lift is created near the nose of the airfoil and making the wing less wide but longer means that the added area in the rear has less effect than adding it at both tips of the wing.
To quote a quite indisputable source, S. Hörner writes in the introduction to Chapter XVII of his book "Fluid Dynamic Lift":

[In low aspect ratio wings] … the chord and curvature are large so that the ratio of the chord [to] the radius of the stream curvature is also large. As a consequence, the airfoil sections lose lift, their sectional lift-curve slope is less than in two-dimensional flow and the lift angle of the average section is increased. Of course, the induced angle is also increased corresponding to C$_L$/A as in larger aspect ratios.

Next, lift curve slope is no longer linear with low aspect ratios. A bit before, S. Hörner says:

The lift curve slope of low aspect ratio wings increase with angle of attack up to the stall angle rather than remaining linear as in the case of conventional wings. The increase in slope is a secondary effect that takes place over and above the basic circulation lift slope.

If you follow the logic explained in this answer, lift curve slope increases with angle of attack because the higher frontal area of the wing at increasing angles of attack will capture more air for creating lift, increasing its efficiency in the process.
With lower lift curve slope, the stalling angle is higher for wings of smaller aspect ratio. NACA Report 1091 contains test results on low aspect ratio wings, and while lift curve slope increases with aspect ratio, maximum lift is roughly constant and even shows larger values at very small aspect ratio.

Since this report is about lateral control characteristics of low aspect ratio rectangular wings, an unusual way of plotting lift coefficient over angle of attack was chosen. See below, also from NACA Report 1091:

The wing with the highest lift coefficient is the one with 45° sweep. Sweep delays the stall angle in addition to the effect of low aspect ratio.
EDIT:
Now for the theory that downwash reduces lift. This is true for the downwash of a wing flying ahead of the wing concerned (as in case of a horizontal tail) but not for the main wing of a standard configuration airplane. What happens past the wing is a consequence of the flow conditions ahead of and over the wing, not vice versa. Causality flows with the air.
What is probably meant by such a theory is that a reduced aspect ratio reduces the vorticity when flow is described as potential flow. I always find it easier and more instructive to use physically tangible phenomena to describe what happens instead of mathematics, so I will not resort to potential flow theory, even though it produces correct explanations, too.
Lift is produced by a wing by deflecting the air in its vicinity downwards. This deflection happens mostly in the forward part of the wing's chord; that is why the neutral point of an airfoil sits at its quarter chord. With smaller aspect ratios this location moves forward until the neutral point approaches the leading edge (better, in that case, the leading point) of slender bodies. These are objects where chord is much higher than span; fuselages or external tanks already behave much like a slender body.
The reason is simple: The pressure difference between both sides of the wing is reduced by flow around the wing tips: Reduce aspect ratio, and this effect becomes relatively larger and reduces lift especially in the rear part of this wing. The neutral point moves forward and the lift curve slope shrinks. Note that this is not the tip vortex but only the equalisation of pressure at the tip. This movement induces a circular flow which will form the tip vortex further downstream, and saying that the tip vortex reduces lift is similar to saying that wet streets cause rain. But I digress …
A reduced pressure difference also means that the pressure rise after the suction peak near the leading edge of the wing is shallower at the same angle of attack than it is for a wider wing of higher aspect ratio. Consequently, it needs a higher angle of attack until the pressure gradient is steep enough to cause the flow to separate on low aspect ratio wings. Since stall is caused by a sufficiently large growth of flow separation so lift stops to increase with angle of attack, a lower aspect ratio wing will reach this stall angle of attack later than one with a higher aspect ratio.

@qqjkztd The twist is optimized for high subsonic speed, but doesn't look so large to me. Besides, with the "living wing" (slats and flaps continuously adjusted) twist will vary with load factor and speed. Conical camber helps at supersonic speeds, so not every twist is bad for supersonic drag. The apex surfaces are the strakes? They create [vortex lift]{https://aviation.stackexchange.com/questions/21069/what-is-vortex-lift/21071?r=SearchResults&s=1|47.2170#21071}, which is also the reason for the high lift of the swept wing here.

@PeterKampf just to clarify from what I understand so far is it that the stalling angle isn’t affected by induced downwash. As so far the information which I could find and from the answer below is it not linked to the tip vortices ? I’m a bit confused now.

@Jai  The tip vortices are responsible for a lot of stuff in Internet lore, but what rally happens is that pressure difference build between upper and lower surface is reduced by the low aspect ratio. It needs more angle of attack for the same difference with a smaller aspect ratio, and consequently stall is delayed as well.

@PeterKampf with respect to this could you provide some more clarity with respect to your answer. As this is an entirely new concept and isn't explained even in Oxfords ATPL set.

@Jai The writings of S. Hoerner are now more than half a century old, so this can hardly be new. If you prefer to restrict your knowledge to what is published in the ATPL test, so be it. Please explain better what clarity is missing – the explanation above is kept as simple as possible.

@PeterKampf I don't want to restrict my knowledge just to Oxfords I prefer to expand my knowledge base as much as possible as a professional pilot I personally feel its important. I can't really understand the theories put forward by S. Hörner. If possible could you help me to understand that because the answer is clearly there but I can't fully understand it.

"The basic principle is that most subsonic lift is created near the nose of the airfoil". This doesn't make any sense. Elongating chord length does not create more area at the rear. Scaling the wing chordwise does not change the pressure distribution at all. This is purely a 3 dimensional effect.

@Jai  Now I added a lengthy explanation but if I don't know what exactly is still unclear I have a hard time improving this answer.

@PeterKämpf "This is true for the downwash of a wing flying ahead of the wing concerned (as in case of a horizontal tail) but not for the main wing of a standard configuration airplane. Causality flows with the air." Is this consistent with fact that pressure changes propagate upstream in subsonic flow?

@user0422 Splitting hairs, ain't we? OK, how about "causality flows with propagating pressure"? Sounds a bit awkward, and since air is moving much less than the plane is, it also only describes a model and not reality.

@PeterKämpf Yes propagating pressure is Ok.  I cant find in theory calculation part where downwash appears ahead of wing, I see only part where downwash is at the wing(which is true for real wing). I am looking at lifting line theory, where is this part or I look at wrong theory?

@user0422 Ahead of the wing it is called upwash. Lifting line is part of potential flow theory, so that should be correct.

@PeterKämpf I know in reality upwash is ahead of the wing, but does this theory at page 13, figure 12.13 show downwash ahead of x (wing)?
https://web.stanford.edu/~cantwell/AA200_Course_Material/AA200_Course_Notes/AA200_Ch_12_Wings_of_Finite_Span_Cantwell.pdf

@user0422 Did you ever try to read the caption? This is only the speed induced by the two free vortices. Upwash is the product of the bound vortex, the effect of which is neglected in the plot. Real flow can only be approximated by adding the effects of all three.

@PeterKämpf I cant find any work how final upwash(after reduction from induced velocity) is calculated. So I post this question: https://aviation.stackexchange.com/questions/96401/how-to-calculate-wing-upwash-angle

A little bit of logic here from what has been learned (generally):

Low aspect wings have lower stall speeds than higher aspect wings.
Rectangular wings stall at the roots.
Tapered wings are prone to "tip stall"
Inboard downwash from wing tip vortex helps delay tip stall
Rectangular (lower aspect) wings (with larger wing tip vorticies) are less prone to tip stall (but would produce more drag than tapered tips in cruising flight).

For equal weight and wing area we have:

Lower aspect wings produce larger wingtip vorticies, requiring more thrust for the same airspeed and AOA.  Higher aspect wings are more efficient.
Larger vortices reduce tendency to tip stall.
Because vorticies delay tip stall, with sufficient warning from root stall "buffet", a pilot could go to a slightly higher AOA and still safely maintain control of the plane but...

It is doubtful lengthening the same airfoil would have a major effect on its stall AOA for a straight wing, without designing something hopelessly chunky with no cruise efficiency (but maybe a good fighter jet).
Then why do lower aspect wings have a lower stall speed?  The answer (as in parachutes) is with improved utilization of "bottom" lift.  Better here to use a square (or circle) as did the sailing clippers of old.
And how does the delta continue producing lift at a higher AOA?  By actually harnessing its vortices along the top of the entire wing, which maintains organized airflow and lift.  Vortex generators are used to the same effect on a straight wing.